This invention relates to data display systems and, in particular, to systems for remotely displaying data such as the time of day.
Previous systems for remotely displaying time of day information basically involve either the parallel or serial transmission of the time data. Typically, in parallel transmission systems, 30 line drivers are required at the sending end with a 30 wire cable connecting the remote read-out to the master generator. Further, the remote display unit requires 30 line receivers with nine, 4-to-10 (for Nixie) or 4-to-7 segment (for LED) decoders depending on the type of display. Also a large power supply is required to operate the logic circuitry in the remote display where as much as 250 volts D.C. is required if gas discharge type read-outs are employed.
In serial transmission systems, a serial code is employed with a frame sync pattern to transmit BCD data in segmented time divisions, requiring sub-frame identification and a modulated carrier. At the remote display, a sophisticated automatic gain control is required to normalize the signal so it can be reliably demodulated. Further, a frame sync detector is required along with frame sync counters, data storage, 4-to-10 or 4-to-7 decoders, along with display drivers, current limiting resistors for each segment and a large power supply with several voltages to operate the logic circuitry. Again, a high power supply voltage (approximately 250 volts D.C.) is needed if a gas display read-out is employed.
It is known in the prior art to transmit data from a first location to a second location over a single line and to send a power signal back to the first location from the second location over the same line. Thus, a data collection system is known wherein a series of remote transmitters are connected to sensors for forwarding data to a central receiver. Power for the transmitters is sent over the line to recharge batteries respectively associated with the transmitters. It is also known to provide a digital compass which is supported by a gimbal assembly which, in turn, is electrically connected to a conductor. Energizing power is supplied to the compass through the gimbal and data for read-out in the same manner. Other telemetry systems and similar systems are also known having a signal line carrying power in one direction and data in the other. However, in none of the foregoing systems are the power and data both transmitted in the same direction to a remote device such as a remote time display.